Geiger tube radiation meter



Patented Feb. 5, 1952 UNITED STATES PATENT OFFICE GEIGER' TUBE RADIATIONMETER James M. Constable, Ozone Park, N.Y. Application November 26,1949, Serial No. 129,543

- solaims. (ci. 25o-83.6)

' The present invention relates to a Geiger tube radiation meter andmore particularly to a meter which is light in weight and has a long*lived power supply.

As the science of nuclear physics advances and the discovery, mining,purification and application of radioactive materials becomes morewidespread both in a civilian and military sense,it becomes increasinglyimportant that simple, rugged, accurate, and lightweight detecting andmeasuring instruments for beta, gamma, and alpha rays and particles bemade available. Heretofore, the most successful instruments were of thetype employing Geiger-Mueller tubes and various types of vacuum tubeamplifying means for increasing the output of the Geiger-Mueller tubessufciently to be readable on a microammeter integrating circuit. Whilethese instruments are far superior to any previously available,` theystill have several serious disadvantages in'that the vacuum tubesrequire both filamentV and plate supply batteries which are ofconsiderable weight because of the added necessity of supplying rela#tively high voltages to the Geiger-Mueller tube therefrom, the vacuumtubes had to be miniaturized to reduce the drain on the batteriesthereby to increase their lives which resulted in adelicate structure,and the vacuum tube amplifiers are both complex and, because of theircomplexity, inaccurate. v

To obviate some of these disadvantages, special small high voltagebatteries have been yprovided for use with these instruments. However,vthe weight of the batteries is still excessive, becausethey arenon-standard they are not readily available so that prospectors forradioactive ores could not secure them in remote localities nor wouldthey be on hand in areas of great emergency as when an atomic bomb hasfallen, and the lives of such batteries by reason of their extremelysmall cell size is short and unreliable.

To eliminate the use of such batteries, special vibrators andtransformers have been developed to convert the output of 3 voltbatteries tothe high voltage necessary tothe operation of a"Geiger-Mueller tube which ranges between 500`- to 1500 volts. lIn thistype of supply, the .battery has one terminal connected to the mid-pointof the primary of the transformer, the other ter. minal of they batterybeing connected toeither, end of the primary alternately by operation ofthe vibrator. The step-up ratio of the turns on the primary andsecondary windings of the .trans-.3 former is proportional to the ratioof the batteryv voltage tothe desired voltage and, because the" 2desired voltage is high, the turns on the secondary winding must alsonecessarilybe high. It is obvious then that such a winding has both highresistance and inductive impedance which leads to large power losses inboth the resistance of the winding and the iron in the transformer core.Because the vibrator has to have its armature driven at its highresonant frequency andwith considerable amplitude in order to swingbetween its two opposing contacts, a considerable mechanical loss isengendered thereby so that it has been found that by reason of the highresistance, magnetic and mechanical losses, this arrangementA has apower conversion efciency of only 5 to 10%. Other arrangements have beenfound to be equally inefficient by reason of the high electrical,magnetic, and mechanical losses inherent in their construction. Thepresent invention was designed after a thorough analysis of theforegoing disadvantages and with a view to producing an instrument thatis simple, rugged, accurate, and requires Asuch low battery consumptionas to be Aboth lightweight and long-lived. These results have beenachieved a' by the total elimination of all filament type vacuum tubeswith the consequent elimination of the necessity for filament supplybatteries and a considerable enhancement in the ruggedness andsimplicity of the arrangement without'any' sacrice of its accuracy. Theaccuracy has been further increased by the provision of specialintegration and calibration circuits whereby both low Ycount and highcount radiations may be indicated with great precision by a simpleswitching between circuits of greater or lesser sensitivity. Furtherreduction in battery weight is accomplished, not only by the eliminationof the lament supply battery, but also by providing a highly eficientpower supply for the Geiger- Mueller tube which likewise serves as thesource of power for such cold-cathode electronic tubes as are foundnecessary to the operation of the instrument. Because of the eliminationof the filament battery and the high efficiency of the main powersupply, battery life is also greatly extended beyond the maximumheretofore achieved. In a final attempt to secure simplicity, the powersupply has been designed to operate from a single standard flashlightcell of the type readily available in any five-and-ten-cent store orcross-roads country store.

Specifically, the apparatus of the present invention comprises aGeiger-Mueller tube having its voltage supply connected thereacross. vAstepdown transformer is so connected to the tube that pulsescorresponding to the tube pulses pass through its primary winding andappear across its secondary winding at considerably decreased voltagebut higher amperage. These low-voltage hgh-amperage pulses are rectifiedand supplied to a microammeter having an integrating condenser connectedthereacross whereby the microammeter will indicate a value dependentupon the number of pulses produced by the tube per unit of time. Theaforesaid rectification can be switched to be either half-Wave orfull-wave, the half-wave rectification having been found to be moresensitive for low tube counts and the full- Wave rectification providinggreater resolution for high tube counts.

For even greater sensitivity when the number of pulses from the tube islow, a storage condenser may be provided across the tube so as toenhance the intensity of the pulses and a variable calibration resistoris provided for simultaneously ad- .I

justing the effective value of the storage condenser and variablyshunting themicroammeter for calibration purposes. When full-waverectication is employed, a second variable resistoris connected to shuntthe microammeter tof'provide calibration thereof.

The novel power supply includesa closed core inductor having a lowresistance primary winding in series with the winding and normallyclosed contacts of a vibrator relay, the series circuit being connectedto a single dry cell of theilashlight type. The inductor is alsoprovided with a fairly low resistance secondary winding connected inseries with a gaseous tube rectier'to a storage condenser, the latter inturn being connected through a loading resistor to a voltage regulatingtube. The voltage regulating tubeis connected through either a surgelimiting'resistor or rectifier to a condenser which'acts as 'the powersupply for the Geiger-Mueller tubeandits associated meter circuit.

An object of the present invention is the y'provision of a radiationmeter in Whichalllamenttype tube amplifiers have been eliminated.

Another object is to provide a radiationmeter having as its only sourceof power a single dry cell of the flashlight type.

A further object of the invention is rthe provision of a high eiciencylow-drain .powerconversion system between a dry cell anda Geiger-Mueller tube.

Still another object is to provide an-amplication means which convertsthe high-voltage'lowcurrent pulses of a Geiger-Mueller tube tolowvoltagehigh-current pulses without the intervention of electronic tubes.

Yet another object of the present invention is the provision in aradiation meter of .readily adjustable circuits which are capable ofdetecting low count pulses from a Geiger-Mueller tube with greatsensitivity and high count pulses with great accuracy.

It is also an object of the invention to provide a radiation meter whichis selectively responsive to both low and high count pulses from aGeiger- Mueller tube with simple calibration means.

A further object is to provide in the power supply system of a radiationmeter, a voltage regulation means arranged to prevent surges produced bysuch regulation lfrom having a deleterious effect on the operation of aGeiger-Mueller tube energized therefrom. Y

Other objects and many of the attendant advantages of this inventionwill be readily apprecated as the same becomes better understood iii-known in the art as Geiger-Mueller tubes.

vof la. 'resistor 4.

4 by reference to the following detailed description when considered inconnection with the accompanying drawings in which like referencenumerals designate like parts throughout the gures thereof and wherein:

Fig. 1 is a diagram of the preferred form of circuit employed in theradiation meter of this invention, and

Fig. 2 is a diagram of a modified circuit intended Vto replacea portionof the circuit of Fig. l.

Referring now to the drawings, there is shown in Fig. 1 a gas-filledtube I of the type which discharges when the gas therein is excited byexternal radiations as from gamma, beta or alpha rays or particles, suchtubes being generally The tube I is vprovided with the usual cathode 2and anode 3. the anode being connected to one end The other end ofresistor 4 is connected to one end of the primary winding 6 of fa.step-down transformer 5, the other end of theprimary winding 6 beingconnected to `one end ofa condenser 'I which has its other end connectedto the cathode 2 and is grounded. The condenser 'I is maintained chargedat the operating voltage of the tube I by power supply equipment to.bedescribed hereinafter and serves therefore as the source of highVoltage for making tube I .operative when radiations excite the gasestherein.

The transformer 5 is of the closed core type, as illustrated, and isprovided with a center tapped secondary winding 8 having considerablyfewer turns than the primary winding 6, a ratio of about 40 to 1 beingpreferred. One end of the secondary winding 8 is connected through arecti-l fier 8 to one end of a microammeter I0, the other endof which-is connected to the center tap of the secondary winding. Connectedacross the S microammeter I0 is an integrating condenser II.

The other end ofthe secondary winding 8 -is connected to one end of asecond rectifier I2, the other end of which isadapted to be disconnectedfrom or vconnected to the same end of the microammeter I0 as is therectier 9 by the switch I3. The rectiers 9 and I2 are poled to producefullwave rectication of the output of the secondary winding 8 when bothrectiers are connected to the microammeter I0.

Connected between the anode 3 andthe resistor 4 is one sid-e of acondenser I5 of much smaller capacity than the power supply condenser 1,the other side of condenser I5 being connected to one end of a resistorI5 havingan 'F- adjustable sliding contact thereon as illustrated.

A second switch I4 mechanically interconnected with switch I3, as shown,to provide simultaneous operation thereof is arranged in its left-handvpositionto connect the sliding contact of resistor I6 tothe groundedlead I8 of the power supply and in its right-hand position to connect asliding contact on a resistor Il to the grounded lead IE for a purposeto be made apparent hereinafter. It vwill be noted that one end of theresistor I'I is connected to one end of the microammeter I8, the otherend of the microainmeter being connected by lead Ia to the grounded leadI8. In its left-hand positionthe switch I3 con-A nects the lower end ofresistor I6 to the end 'of the microamm'eter I0 which is not connectedtov lead IBa.

In order to maintain the condenser 'l chargedat a high voltage, avoltage conversion and regu. lating system energized from a single drycell I8. whichfmay be ofv the flashlightlcattery or equ,iva-.

lent low voltage, lightweight type, is provided. The voltage conversionV'portion of Vthe system comprises a relay 2li having a coil andnormally closed contacts in Vserieswith the battery IS' and the primarywinding 22 'of an inductor 2l, the inductor having a closed core 30 anda secondary winding 23 thereon. l

The relay 20 is a current operated relay'A designed so that a minimumarnountrof power is required to eiieet opening of its contact, andthemechanical movement of the relay armature need be very slight and onlygreat enough to break the contact as, distinguished from the operationof the usual full-wave vibrator which must have suiiicient mechanicalmovement in its' armature to close a pair ofback contacts. It isapparent that this type of construction reduces the battery drainconsiderably over other arrangements. I

The primary winding 22 has very few turns and therefore low resistanceloss to limit further the drain on the battery I9, the high induotanoeof the closed core 38 providing considerable magnetic energy storagetherein to cause the primary winding 22 to have a large impedancetherebyto slow down operation of' the relay 20 with'a further saving ofmechanical energy and consequent reduction of the drain on battery I9.Opening of the contacts of relay 20 produces a large magnetic surgethrough the core 30 and this produces in the relatively few turns oflthe winding 23 a considerable voltage which is greater than the`magnitude needed to operate the tube I'. The ratio or the turns ofprimary windingl 22 tosecondary winding 23 need not approach li that ofthe ratio of the voltage of battery I"9 to that needed to operate'tube Ias the voltage' produced by winding 23 is not onlya function of'itsturns but also of the rate ofV change of v'fluir in core 30 which, asstated above, is very high. The use of a closed core provides highinductance and eliminates the losses inherent in an open core wherebythe size and weight of the core'can be made quite small. Thus the weightof inductor 2.! is considerably reduced v`when compared with that of astep-up transformer or an open core induotor.

The secondary Winding 23 has one side connected to grounded lead I8 andtheotlier side is connected to the anode of' a cold-cathode, highvoltage rectier 2li, the cathode of which is connected to one side of acondenser 25 having its other side connected to grounded lead I8.Connected across the condenser 25 isa voltage regulator ltube 25 of theionization type having an anode 28 and a cathode 2i connected togrounded lead I8, `a current limiting resistor Z9 being arranged in thecircuit between tube 26 and condenser 25. The resistor 2S andthe tube 26act to produce a load on condenser 25 which limits the peak voltage onthe latter and therefore thel voltage across the turns ofsecondary'winding 23 and primary winding 22, the number of turns 'onwinding 22 being selected to limit the voltage across the contacts ofrelay 2B to a safe value.

to prevent impropereperation thereof.

i'f desired, the anode 28 may be connected directly to the primary 5. oftransformer thereby to eliminate the condenser 'i but it has `beenfound.. more desirable to employ the'condenser I-V to'reduce the eiectofsurges likely'to` b'e produced bythe voltage regulator tube 25 whenthevoltageY of battery I9 is low. To achieve this result, the condenser Iis connected through a rectiiier 3| across the tube 26,- the4 rectierbeing Tir poled soth'at surges vfrom the-tube 26 arei'solated fromcondenser 'I'. When Geiger tubef i ispulsing to cause thereby'a drain onthe power supply anda drop inits voltage during eachpulse, the regulatortube `will momentarily stop conducting fdurin'g' each` pulse if thebattery 'voltage is low rand asurge will result when conduction resumes.This surge is blocked by rectifier 3l which acts as a low resistance inone direction and a high resistance in the other permitting therebycharging of condenser 'I but opposing the eiiect of surges. If desired,rectifier 3| may be replaced by a resistor which will permit condenser'I to supply the peak currents while the condenser need supply only anaverage current to the condenser 1.

Referring now to Vthe arrangement of Fig. 2, there is disclosed thereina modification in all respects similar to'that ofFig. 1 except that theprimary Winding 6 of transformer 5 is connected in series with condenserI5 across the tube I, it" being apparentfthatdisoharges of tube I` willproduce pulses in secondary winding 8 in a manner 'similar to thearrangement of Fig. 1.

The :operation of the radiation meter described hereinabove will now bedisclosed. Referring to Fig. l, as soon as the battery I9 is connectedin circuit' as by a switch, the relay 2U commences to vibrate producingthereby intermittent high intensity iiux surges in the closed core ofinductor 2l whenever the contacts Yof relay 26 open, it being apparentthat the building up or' the flux in core 30 is relatvely'slow when thecontacts close. These high intensity flux surges link the turns ofsecondary winding 23 to prod-uce' high Voltagev pulses therein which arerectitled by 'rectiiier 24, the direction of winding 23' and poling ofrectier 24 being arrangedto permitthis. Tlie'intermittent'high voltagepulses charge the 'condenser 25 to a voltage determined by the voltageregulator tube 26 and the loading resistor 29, such voltage being of amagnitude to produce vdischarge of the Geiger tube I in the presence ofradiations. The condenser 25 vgradually charges the condenser 'I throughthe resistance of4 the'rect'ier 3l, or a resistonwhich maybevsi'ibstitutedtherefor as described above, the voltageof` thecond'enser'l remaining substantially constant th-erec'tiiier 3l. Y

The meter is now ready for calibration, it beingmerely necessary toselect the positions ofi switchesv i3 and I li and set the calibrationof' resist'cnrsv 'I6' or I'I 'depending on whether a low of a. Ahighradiation count is to be detected.

Assuming that a low radiation count is to be detected, it is obviousthat the instrument shouldV Y have high'sensitix'fity even at thesacrifice of good resolution. For high sensitivity, the switches I 3 andI4 arethrown to the left or into `the position shown in `vlig. 1", inwhich position the condenser I5 is connected in series with a portion ofresistor IG and through its movable contact and the switch I4 to thegrounded lead I8. It is thus apparentv thatthe condenserV and theupp'erpoition ofv resistor I6 are connected across the anode and cathodeof tube I and that the cha'rge inthe condenser will'be discharged, whenthe tube I becomes conductive, at a rate determined by the poitionofVthe resistor I6 in lseries witlii the? ciziiidenser.l It will beapparent, also, that the'condenser t5' acquires its chargefr'om thecondenser Ithr'ough the andcurrent limiting resistor 4L vWithr theswitchv` I3-thrown to' the left,-V the by reason ci.v the 'presence ofprimary winding 6"' rectifier 9 only is connected to the microammeter Iand the lower portion of resistor I6 is oonnected across themicroammeter by means of leads I8a and I8 and switches I4 and I3. Itwill be noted that when the adjustable tap on resistor I8 is moveddownwardly to increase the amount of resistance in series with condenserI and thus decrease its rate of discharge and therefore the size of thepulse passing through primary winding 6, the amount of resistanceintroduced by resistor I6 across the microammeter I0 is reducedsimultaneously to increase the shunt across the microammeter thusreducing its sensitivity. Thus, resistor I8 acts as a calibration meansand it may be so adjusted when a standard source of radiations is placedadjacent Geiger tube I to provide any desired scale reading onmicroammeter I8.

The condenser I5 is a recognized means for increasing the pulse size ofthe Geiger tube when greater sensitivity is desired as it is obviousthat it permits an enhanced discharge across the Geiger tube by reasonof the charge stored in the condenser. An additional increase insensitivity is achieved by the use of half-wave rectification inemploying the rectifier 9 alone as this leads to pulse stretching in thewinding 8 of transformer 5 by reason of the inductive lag in the core ofthe transformer when the entire pulse passing through the core is notutilized. Because of the latter means for securing greater sensitivity,the condenser I5 may be omitted.

From the foregoing, it will be understood that the meter is firstcalibrated against a standard source and that when the tube I is placednear a source of low count radiations, the pulses passing throughprimary winding 6 will induce pulses of a considerably higher amperagebut lower voltage in the output of secondary winding 8 of transformer 5which are rectified by rectifier 9 and integrated by condenser II toproduce an average reading on the microammeter I0, the latter beingproperly calibrated to give a direct reading of the number of radiationsreceived by the instrument.

For higher count radiations, the switches I3 and I4 are thrown to theright, thereby disconnecting condenser I5 and resistor I6 from thecircuit but connecting rectifier I2 to the microammeter Ill to providefull-wave rectification of 'the output of transformer secondary Winding8, the calibration resistor II being also connected across themicroammeter. The removal of the condenser I5 lowers the sensitivity ofthe meter but sensitivity is unnecessary when high radialtion counts areto be detected. Likewise, as soon as the output of winding 8 isconnected for fullwave rectification, the inductive lag in the core oftransformer 5 is eliminated along with the pulse stretching producedthereby with a consequent reduction in sensitivity, now no longernecessary, but with a corresponding increase in resolution so that eachpulse will produce a definite eect on the integrating condenser I Ithereby to increase the accuracy of the readings of microammeter I8. Asbefore, the calibration of the meter is determined by a standard source,the resistor I1 being adjusted to produce a desired initial reading onthe microammeter.

The operation of the modification of Fig. 2 is essentially the same asin Fig. 1. The condenser I5 is charged from the power supply throughresistor 4. When Geiger tube I discharges by reason of radiationsimpinging thereon, the discharge of' condenser I5 causes a high-voltage.

low-amperage pulse to pass through primary winding 6 and produces alow-voltage, high-amperage pulse in secondary winding 8 which isrectiiied by rectifier 9, integrated by condenser II, and indicated bymicroammeter I8. As in Fig. 1, full-wave rectification may be employedfor the output of secondary winding 8 and the various calibration meansdisclosed in Fig. 1 may be employed.

From the foregoing description, it will be apparent that a radiationmeter has been provided which is simple, lightweight, and has Very fewparts while maintaining great efficiency and accuracy in its operation.Tests have shown that its power conversion efficiency is in theneighborhood of 40% whereas the highest previously known for this typeof supply is 17%. The unit is so efficient that 70 hours of operationmay be expected from one standard ashlight battery Whereas heretoforetwice the weight of batteries in other arrangements has given less than8 hours of operation.

The power supply is inherently self-regulating in that when the batteryvoltage drops, the output high voltage does not drop in proportion asthe relay 20 merely slows down but continues to produce practically thesame induced voltage in the secondary winding 23 of the inductor 2I, anydrop in voltage being produced merely by the demands on the charge incondenser 25.

The tube I does not necessarily have to be a Geiger-Mueller tube as anycounter tube which operates to produce small pulses may be employed inits stead. The indicating means need not be restricted to themicroammeter I0 and the integrating condenser II as these may bereplaced by other indicating or recording means satisfactory for thepurpose.

Various modifications are contemplated and may obviously 'be resorted toby those skilled in the art without departing from the spirit and scopeof the invention, as hereinafter defined by the appended claims as onlypreferred embodiments thereof have been disclosed.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. A radiation meter comprising a gas-filled tube subject to dischargeby radiations when energized, a source of electric power supply forenergizing said tube, a step-down transformer having a primary windingand a secondary winding, said primary winding being connected to thesource of power supply for said tube and responsive to the discharge ofthe latter, an indicating means connected to said secondary winding andenergizable therefrom for indicating the rate of discharge of said tube,and a rectifier interposed between said secondary winding and saidindicating means to supply the latter with unidirectional current.

2. A radiation meter comprising a gas-filled tube subject to dischargeby radiations when energized, a source of electric power supply forenergizing said tube, a step-down transformer having a primary windingand a secondary winding, said primary winding being connected to thesource of power supply for said tube and responsive to the discharge ofthe latter, an indicating means connected to said secondary winding forindicating the rate of discharge of said tube. a rectifier interposedbetween said secondary winding and said indicating means to supply thelatter with unidirectional current, and an integrating condenserconnected across said indicating means and in series with saidrectifier.

3. A radiation meter comprising a gas-filled tube subject to dischargeby radiations when energized, a source of electric power supply forenergizing said tube, a step-down transformer having a primary windingand a secondary winding, said primary winding being connected in serieswith the source of power supply for said tube and responsive to thedischarge f the latter, an indicating means connected to said secondarywinding and energizable therefrom for indicating the rate of dischargeof said tube, and a rectier interposed between said secondary windingand said indicating means to supply the latter with unidirectionalcurrent.

4. A radiation meter comprising a gas-filled tube subject to dischargeby radiation when energized, a source of electric power supply forenergizing said tube, a step-down transformer having a primary windingand a secondary winding, said primary winding being connected to thesource of power supply for said tube and responsive to the discharge ofthe latter, an indicating means connected to said secondary winding forindicating the rate of discharge of said tube, a rectifying arrangementinterposed between said indicating means and said secondary Winding forproducing half-wave or fullwave rectication of the output of thesecondary winding, and switching means operable for selectivelyconnecting said indicating means to said rectifying arrangement tosubject said indicating means to half-Wave rectication for low rate tubepulses and to full-wave rectification for high rate tube pulses.

5. A radiation meter comprising a gas-filled tube subject to dischargeby radiation when energized, a source of electric power supply forenergizing said tube, a step-down transformer having a primary windingand a secondary winding, said primary winding being connected to thesource of power supply for said tube and responsive to the discharge ofthe latter, an indicating means connected to said secondary winding forindicating the rate of discharge of said tube, a rectifying arrangementinterposed between said indicating means and said secondary winding forproducing half-wave or fullwave rectification of the output of saidsecondary winding, switching means operable for selectively connectingsaid indicating means to said rectifying arrangement to subject saidindicating means to half-wave rectication for low rate tube pulses andto full-wave rectification for high rate tube pulses, and an integratingcondenser connected across said indicating means and in series with saidrectifying arrangement.

JAMES M. CONSTABLE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,920,569 Koros Aug. 1, 19332,026,421 Fecker Dec. 31, 1935 2,225,700 Laing Dec. 24, 1940 2,231,873Barrett Feb. 18, 1941 2,401,723 Deming June 11, 1946 2,474,581 HowellJune 28, 1949 2,531,106 Brown et al Nov. 21, 1950 OTHER REFERENCESNucleonics, Oct. 1948, pp. 52 and 55.

